Introduction to Computer Networking

1. Introduction to Computer Networking Networks, Devices, Bandwidth MM Clements

2. Last Week ………… • Shared Ethernet needed rules to avoid collisions on the network - CSMA/ CD • Switched Ethernet does not allow for collisions so CSMA/ CD not needed Implemented for backward compatibility • Very little difference between Ethernet and IEEE 802.3 or their respective frames ITCN

3. This Week • Networking Devices • LAN, MAN, WAN, SAN • Virtual Private Networks (VPNs) • Bandwidth – importance and calculations • Units of bandwidth and storage • Layered models – OSI • Importance to networking ITCN

4. Network Basics • Early 1980s saw the PC and early networks • After Lotus Notes, business wanted the PC • Data generated needed to be shared • PC connects to network with a NIC • NIC has a hardware address as supplied • Identifies PC on a LAN • LANs needed interconnection to each other • Needed the router - developed by Cisco • Led to development of MANs and WANs ITCN

5. LAN & WAN devices • LAN types – Ethernet, Token Ring, FDDI etc. • Composed of hosts, hubs, switches, routers • WANs and MANs join distant LANs together • Use Routers, communication servers, modems, CSU/ DSUs, TA/ NT1 • Allows LANs to have access to www, email, FTP, real-time services etc ITCN

6. Topologies for LANs ITCN

7. Local Area Networks • Covers a small area e.g. school, one floor of an office block, small group of buildings • High internal data rate e.g. 100Mbps or more • Cabling and equipment owned by LAN owner • Ethernet over twisted pair and WiFi are the most commonly used technologies for LANs today ITCN

8. Metropolitan Area Networks, MANs • Connect LANs in a town or city using high data rate links for one company • Use ATM, FDDI but largely being replaced by Metro Ethernet • Virginmedia (formerly Telewest) and NTL use MANs to distribute TV and broadband service • Often owned and operated by a single organization • usually used by many individuals and organizations • may be owned and operated as public utilities ITCN

9. Wide Area Networks, WANs • Have a global scope potentially • The Internet is the biggest WAN • Created to join separate networks together • Generally lower data rate than LANs • Cabling owned by WAN operator e.g. ISP • Bandwidth is rented or leased by end users • Built using leased lines, circuit switching, packet switching, cell relay technologies • Connect to LANs etc using router plus line card ITCN

10. Storage Area Networks, SANs • Storage Area Network used to join servers and high capacity storage devices together • E.g. disk arrays, tape libraries • Used mainly in large computer installations • Similar idea to NAS – used in smaller LANs e.g. SOHO to provide access to single files e.g. mp3s, video files to end devices ITCN

11. Virtual Private Networks (VPNs) • E.g. VPN formed between work and home • Secure ‘tunnel’ formed across public network • 3 Types: • Access VPNs • Intranet VPNs • Extranet VPNs • Maintain companies’ security policies ITCN

12. Intranet and Extranet • Intranet uses TCP/ IP and has web servers etc. • Content only visible to employees at work • Extranet extends intranet to authorised people e.g. teleworkers • Passwords, authentication etc. required to connect to extranet ITCN

13. Building a LAN • Need at least two hosts – e.g. PC and Xbox • These need Network Interface Cards/ Devices • Need interconnecting device e.g. switch • Need cabling or wireless to interconnect devices • Need gateway device on and off LAN – router • Each is defined by OSI model ITCN

14. Cabling or Physical Medium • Belong at physical layer of OSI model • Can be copper or optical fibre or wireless • Commonly used copper cabling: • Category 3 originally used rated at 10 Mbps • Category 5 (Cat5) followed with better properties – rated for 100Mbps • Cat 5e improved on Cat5 for crosstalk • Cat 6 and Cat 7 used for data rates over 1Gbps ITCN

15. Copper Cabling Standards1 • Cat 1: Previously used for POTS telephone communications, ISDN and doorbell wiring. • Cat 2:  Previously was frequently used on 4 Mbit/s token ring networks. • Cat 3: Historically popular for 10 Mbit/s Ethernet networks. • Cat 4:  frequently used on 16 Mbit/s token ring networks. • Cat 5. frequently used on 100 Mbit/s Ethernet networks. • Cat 5e:  often used for both 100 Mbit/s and 1000BASE-T • Cat 6:  Defined of up to 250 MHz, more than double category 5 and 5e. • Cat 6a: . Provides performance of up to 500 MHz, Suitable for 10GBase-T. • Cat 7: This standard specifies four individually-shielded pairs (STP) inside an overall shield. Defined up to 600 MHz. • Cat 7a:  Defined up to 1000 MHz. ITCN

16. Repeaters and Hubs • Belong at physical layer of OSI model • Repeater cleans and boosts digital signals • Multiport repeater known also as hub • Many PCs can connect to hub or switch • Uses a patch cable from NIC to hub or switch • Has RJ-45 plug on each end of Cat 5 cable • Cat 5 cable is twisted pairs of copper wire ITCN

17. Bridges and Layer 2 Switches • Belong at Layer 2 of the OSI model • Bridges (old) were the precursor to the switch • Layer 2 switch is more intelligent than a hub • Switches form a direct connection across backplane between communication devices • Hubs just share the arriving signals (not good for security or overall network bandwidth) • Intelligent switches can form VLANs ITCN

18. Routers & Layer 3 Switches • Belong at Layer 3 of OSI model • Routers sit at edge of a LAN to direct traffic on and off the LAN • Also sit on backbones to direct network traffic • Can connect LAN to a WAN for global comms • Can translate different network formats e.g. Frame Relay to Ethernet • Cisco make most of the world’s routers ITCN

19. Networking Symbols • A few basic symbols exist • Learn these to enable drawing of a network • Quick sketches are extremely useful • Many more symbols exist for more complex network devices • No need to learn them all now ITCN

20. ITCN

21. A Simple Network using Symbols ITCN

22. Bandwidth • Neither infinite nor free – must be conserved • Helps to analyse and design and understand different networks • Demand for BW ever increasing – VOD has caused huge demand e.g. iplayer, 4oD • Can be likened to roads or pipes • Narrow road/ pipe carries little (low BW) • Wide road/ pipe carries lots (high BW) ITCN

23. Measured in bits per unit time (bps, kbps etc) Don’t use ‘speed’ when comparing BWs Proper term is ‘data rate’ Data travel at the same speed in cables Higher BW allows more data to travel at once Likened to a wider road with more lanes Cat 5e cable allows 100Mbps over 100m (max) Fibre optic allows Tbps over 1000s of miles Crosses oceans with optical repeaters BW Measurement ITCN

24. BW of Various Data Connections • Modem & twisted pair = 56 kbps • Ethernet – 10Mbps, 100Mbps, 1Gbps etc. • WiFi 11Mbps, 54Mbps, 300 Mbps • DSL 128 kbps up to 6 Mbps • ISDN 128kbps • Frame relay 56 kbps to 34.368 Mbps • T1 (USA) 1.544 Mbps, T3 44.736 Mbps • E1 (Europe) 2.048 Mbps, E3 34.368 Mbps • OC-1 51.840 Mbps, OC-3, OC-12, OC-48 OC-192 etc ITCN

25. Throughput • Doesn’t ever reach bandwidth for end users • Depends on other traffic on LAN, WAN • Type of data, network topology • Time of day • User (client) computer • Server (remote) computer providing service • Throughput is what you actually get rather than which ‘speed’ the network is rated at ITCN

26. Time for Data Transfer • Time (theoretical) = bits of data/ bandwidth • Time (actual) = bits of data/ throughput • E.g. to transfer 5 MB file over modem link (theory) • 5 x 8 x 1024 x 1024/ 56000 = 749 secs • Same transfer over ADSL 512 kbps • 5 x 8 x 1024 x 1024/ 512 000 = 81.9 secs • Over 10 Mbps Ethernet • 5 x 8 x 1024 x 1024/ 10 000 000 = 4.2 secs • How long would this transfer take at 100 Mbps? ITCN

27. Summary • LAN, MAN, WAN, SAN each suit a particular group’s data requirement • Many devices exist for networking • Hubs, switches, routers, modems, cables etc. • All have a maximum bandwidth • BW is measured in bps Mbps Gbps etc. • Throughput is moderated by real world factors ITCN

28. References 1http://en.wikipedia.org/wiki/Category_5_cable ITCN